notebook gps system

Has anyone experience of a notebook gps navigator system with the usb plug in aerial. My trobles are it works fine, then says it cannot find signal or cannot connect to port. If you go to the settings they have been cleared. You shut down the notebook and you get application or runtime error messages.(windows xp)Through it on the back seat of the car in disgust and give it one more try next morning. Guess what it works fine...close system down..drive off...stop in layby to check position and the troubles are back. Any ideas at all please.